"If Trump is the most racist president in American history, what does that say about all of the other presidents who owned slaves?," Hynes wrote.

"Wait, owning slaves doesn't make you racist," Horn commented.

He went on to say that "owning slaves wasn't a decision predicated on race but on economics. It's a business decision."

Horn doubled down on his remarks in a statement to HuffPost on Thursday.

"Human beings have been owning other human beings since the dawn of time," Horn said. "It's never been about race."

He clarified that "it's never okay to own another person," but added that his comment was regarding "a period of time when that was how you survived, that's how you fed your family."

"It wasn't 'I want to own a black person today,'" Horn said of his comment. "It was, 'I need to feed my family. I need five guys who can work stupidly long hours in the sun without killing themselves."

New Hampshire Republican state committee chairman Stephen Stepanek told HuffPost that "Representative Horn is wrong and his comments are not based in our platform's belief in free people, free markets and free enterprise. Slavery throughout its history in the United States was a racist, inhuman, and immoral practice."

It's estimated that millions of people died unjustly during the Trans-Atlantic slave trade, which brought over 10 million people to North and South America from Africa as slaves. In the US, a well-documented system of racist law and science was used to legitimize the slave trade by painting black people as inferior.